This invention relates to transparent, paramagnetic polymer compositions having rare earth ions complexed with the polymer. This invention particularly relates to transparent, paramagnetic polymer compositions comprising non-ethylene-containing polymer and rare earth ions. This invention also relates to optical fibers or waveguides that comprise transparent, paramagnetic polymer that has a magnetic mass susceptibility greater than 20xc3x9710xe2x88x926 electromagnetic units per gram (emu/g) measured at 298xc2x0 K. This invention further relates to optical switches that contain an element that is comprised of a transparent, paramagnetic polymer having a magnetic mass susceptibility greater than 20xc3x9710xe2x88x926 emu/g measured at 298xc2x0 K. This invention further relates to use of a transparent, paramagnetic polymer for transparent marking, labeling or identification purposes.
It is known that certain rare earth elements have a strong paramagnetic response. This paramagnetic behavior arises from a large number of unpaired electrons in the element""s 4f-electron shell. Because the effect is related to the arrangement of 4f electrons, which are largely unaffected by neighboring elements within a rare earth compound, the general trend across this series of elements can be seen by looking at either the oxides or sulfides of the series. Both the oxides and sulfides in this series involve rare earth cations in the +3 oxidation state.
Based on the data in Table 1 below, taken from CRC Handbook of Chemistry and Physics, 66th ed., p. E116, the strongest paramagnetic effect, as defined by the magnetic mass susceptibilities of the elemental compounds, can be seen as confined to elements 64 to 69 (Gadolinium, Terbium, Dysprosium, Holmium, Erbium, and Thulium).
Merely blending rare earth oxide or sulfide particles within a polymer matrix would produce a filled polymer material that possessed a paramagnetic response. However, since the particles are larger than most wavelengths of light, the filled system would scatter incident waves of light resulting in a material that is not transparent.
Rajagopalan, Tsatsas and Risen, Jr. have prepared ionomers of ethylene acrylic acid (EM) copolymer and ethylene methacrylic acid (EMA) copolymer, in which the copolymers were neutralized with Dy+3, Er+3, Sm+3, Tb+3, Tm+3, and Yb+3, and mixtures thereof. See Rajagopalan, et. al, xe2x80x9cSynthesis and Near Infrared Properties of Rare Earth Ionomerxe2x80x9d, Journal of Polymer Science: Part B: Polymer Physics, vol. 34, 151-161 (1996). They report that these ionomers have valuable optical properties and they exhibit strong Raman scattering and luminescence in the near IR region, which is where most optical communication occurs. Paramagnetic response of such compositions was not considered or even noted.
Polymers containing lanthanide metal ions, specifically Eu3+ and Tb3+ salts are disclosed in Y. Okamoto, xe2x80x9cSynthesis, Characterization, and Application of Polymers Containing Lanthanide Metalsxe2x80x9d, J. Macromol. Sci.-Chem., A24(3and4), pp. 455-477 (1987). The polymers used include poly(acrylic acid), poly(methacrylic acid), partially sulfonated or carboxylated styrene, styrene-acrylic acid copolymers and methyl methacrylate-methacrylic acid copolymers. The fluorescent intensity of these polymers was studied. The polymers made appear to contain up to 8 wt. % Tb3+ and up to 10-11 wt. % Eu3+, though the fluorescence intensity for the Eu3+-polymer salts reached a maximum at 4-5 wt. % Eu3+ content.
It would be useful to obtain a transparent polymer that exhibits a paramagnetic response. Such a polymer would be extremely useful in optical fiber communication systems (e.g., as an optical switch), in transparent markers or labels, or in a number of other potential uses (e.g., for use in separations and assays of bio-active materials, though transparency may not be necessary in such uses, and for living hinges).       Uses  of  Polymer  Compositions        Optical  Switches  
In recent years the proliferation of data communications has placed a significantly increased demand on transmission bandwidths. Optical systems have a much larger bandwidth than electric (metal conductor) transmission systems, and with it the ability to transmit a much greater volume of data through a single transmission line. Optical fibers are therefore the most promising systems for achieving high data rate telecommunications.
Optical fibers are well known for the transmission of light along a length of filament by multiple internal reflections of light. Great care is taken to minimize light losses due to absorption and scattering along the length of filament, so that light applied to one end of the optical filamentary material is efficiently transmitted to the opposite end of the material. An optical fiber is in essence a small diameter waveguide comprising a light transmission portion or core of optical filamentary material, surrounded by cladding having an index of refraction lower than that of the core, so as to achieve total internal reflection along the length of the filament. Optical fibers are known to be made from both organic and inorganic glasses, the glass core surrounded by a thermoplastic or thermosetting polymer, or wholly thermoplastic polymers, that has an index of refraction less than that of the fiber core.
Connectors are important components in optical fiber communication systems. With the increasing use of optical fibers and associated optoelectronic devices such as lasers, light-emitting diodes (LEDs), photodetectors and planar waveguide devices, there is an increasing need for reliable optical connectors, optical switches and aligners.
Switches in optical fiber communication systems are used to change the optical path, e.g., to select transmission lines. In switches and other connectors, the precise alignment of optical paths, either permanently or reconfigurably, between two mating devices is essential for maximum optical coupling efficiency. For example, in the interconnection of a single mode optical fiber, the alignment tolerance must be on the order of a few micrometers or less. There is also a need for devices that can introduce precise, controllable, misalignment of optical paths. Such devices can be used to attenuate lightwave signals. Variable optical attenuators are increasingly important in dense wavelength-division multiplexing (DWDM) optical fiber transmission systems. Variable attenuators are used to vary the amount of loss light experiences as it passes through the device. A variable attenuator based on coupling loss is typically composed of two fibers whose separation is mechanically controlled. As the separation between fibers increases, the amount of loss also increases. Variable attenuators based on polarization loss are composed of GRIN lenses to collimate light from the fiber, a plate or cell to rotate the polarization of the light, and a polarizer to introduce the loss. In-line variable optical attenuators using magnetically controlled displacement are disclosed in U.S. Pat. No. 6,102,582 (Espindola et al.). It would be desirable to obtain the alignment of optical devices swiftly, accurately without physical/mechanical contact needed to move fibers and the like, and to allow for alignment in multiple directions.
Another drawback of optical signals and optical systems is that they do not have the flexibility of electrical signals in regard to their ability to multiplex with other optical signals. Even in optical transmission systems, information signals are generally converted from the optical domain to the electrical domain at the input side of the switching systems, so that signals may be separated and recombined as desired. Then the electrical signals are converted back to the optical domain on the outgoing side of the switching system. This multiplexing and de-multiplexing, therefore, has traditionally been performed using electrical components.
Optical switches and their use are generally known in the industry to those skilled in the art and U.S. Pat. Nos. 5,559,909, 6,102,582, 6,137,608, 6,094,293, 5864643, 6,002,819, 4,946,236 are included by reference in their entirety for further general guidance for those skilled in the art. There is a need not taught or suggested in these references, however, for optically responsive devices that employ transparent, paramagnetic elements.
There is a well-recognized need for marking, labeling and identification purposes, such as those used for product identification, product tracking and anti-theft applications. Such labeling generally is readily detectable by visual means. Bar codes such as are conventionally used in many commercial applications today would be an example of such visible labels.
Some labels are detectable by means other than visual ones. For example, use of magnetically responsive marking technology is generally known in the marking industry. Such magnetically responsive marking is disclosed in U.S. Pat. Nos. 5,560,970, 6,106,089, 5,986,550, which are included in their entirety for further illustration and guidance for those skilled in the art. But, these magnetically responsive markings are still visible and can be obtrusive. Thus, there is a need for markings that are also transparent, that is not readily visible to persons.